The field of the invention is that of reflectors, warning lights and illumination lights together with their interconnection system as used by pedestrians and on bicycles or other small vehicles.
Present day vehicle tail lights utilize an incandescent filament bulb inside a mirrored cavity with a red lens covering the assembly. The mirrored surface is utilized to direct a substantial amount of light into a relatively narrow angle beam corresponding to the direction of the approach of following vehicles. Additionally, the lens gives the light its recognizable red color. Power for the lamp, in the case of a bicycle, is commonly from a 3 watt generator energized by way of the rotation of a wheel and is portioned 0.6 watts for the tail lamp and the remainder for the headlamp. However, this is in stark contrast to the automobile where just one side of its system would typically use ten times this amount of power.
Mechanically, the typical bicycle requires one-tenth of a horsepower from its rider for a speed of 12 mph and this is the equivalent of 75 electrical watts. Tests on the drag created by bicycle generators and published in the literature indicate that they require the equivalent of 15-33 watts additional effort, or 20-44% of the 12 mph effort--a considerable amount. In order to minimize size and weight, a properly designed generator would maximize the output power which implies that the electrical power lost internally and the power lost to mechanical drive coupling would equal the power delivered to the light system. Hence an improved generator which produced 30 watts of drag would have an output power of 10 watts. While this might be a significant improvement, this is still drastically less than the power typically involved in motorcycles and automobiles. Additionally the generator powered light system also has a serious drawback in that the lights are out when the bicycle is stopped and this can be a situation in which they are most needed for safety.
There has been some attempt to use rechargeable batteries to provide the power rather than relying on what can be conveniently generated by the rider, however in the prior art the result has been a system which is bulky and expensive, as well as inconvenient to mount and maintain. These are most generally useful to commuting cyclists whose schedule and need for lighting are non-varying rather than for the casual or juvenile cyclist. Systems which use dry batteries are relatively inexpensive and are convenient to mount and maintain by casual or juvenile cyclists; on the other hand, lights powered by dry batteries are usually of low power to obtain longer service life which makes them much less conspicuous and less safe.
Retro-reflectors, which operate to redirect the light from a source back to the source but do not have to be exactly aligned as would a mirror, require no power from the vehicle on which they are mounted for operation and by utilizing the higher intensity headlamps of an approaching vehicle can under usual conditions be seen at the necessary distances. Thus they are required by the governing authorities for night riding and also are generally accepted by the bicycling population. The ones commonly in use today are molded of a transparent plastic but have a translucent color of red for the rear, amber for the pedal positions and crystal meaning colorless for the front. They are smooth on the side facing in the direction of the light to be reflected which makes for easy cleaning, the other side having a pattern of multiple cube corners. This patterned side which causes the retro-reflection is protected from dirt and moisture condensation by a second molded piece which is glued to the first and forms an isolated air space.
The CPSC (Consumer Product Safety Commission) has set minimum standards for the reflectors that can and must be used on bicycles sold and used in the United States. This has resulted in the development of a very inexpensive unit which is rugged and not overly large owing to improvements in the manufacture of cube-corner retro-reflectors. The CPSC requirements ensure that the various approach angles of bicycle and automobile are taken care of through the specification of performance at large angles of retro-reflector horizontal orientation while mounting is held to a maximum of 5 degrees either up or down in the vertical. Because of the relatively large flat area of the face of the retro-reflector it is not unreasonable to expect the average cyclist will be able to maintain his retro-reflectors in a suitable orientation with only casual observation of their mounting position relative to the bicycle frame.
Helmut Zwahlen on the basis of studies performed at Ohio University has proposed that bicycle tail lamp requirements be adopted which dictate a two candlepower output for a red beam which spans 20 degrees in the vertical orientation and 40 degrees in the horizontal. He theorizes that such requirements could be met with a highly efficient sealed beam approach that would consume one watt of electrical power. He bases the two candlepower requirement on test results which indicate that a point light source tail lamp needs to be 1000 times brighter than minimum detectable brightness for laboratory type conditions of a uniform background with uniform illumination. The applicant has tested, to determine typical values, the rear tail lamp of three present day better quality bicycle generator sytems and found that they project rectangular shaped beams which have about 20 degrees of horizontal dispersion and 11, 13 and 20 degrees of vertical. Unlike the retro-reflector the orientation of the housing by casual inspection is much less satisfactory and the proper method is to energize and project the tail lamp onto a wall so that the mounting can be adjusted to make the height of the projected beam the same as the mounting height of the lamp on the bicycle. A task which is complicated by the lack of generator output when the bicycle is stationary. Given the average cyclist's unwillingness to give much consideration to lighting systems which are typically used infrequently, it seems unlikely tail lamps with precisely focused beams represent an adequate solution.
If a motor vehicle is following another motor vehicle, the driver may or may not be aware of a vehicle ahead of the one he is following. However because he will soon pass a slower moving bicycle, he does need to be aware of a rider along the edge of the road whose retro-reflector and tail light may be obscured by the motor vehicles ahead of his own. Clearly if safety were the only requirement then the system which appears in U.S. Patents in abundance would also be commonplace on our streets. These systems place an omnidirectional light source above the rider at a height sufficient to be seen above adjacent automobile traffic, this usually being accomplished by a pole attached to the rear of the bicycle. One of these by Lewis (U.S. Pat. No. 4,088,882) offers substantially increased light output through the use of a flourescent bulb, even when compared to the new halogen type incandescent.
But power alone does not ensure conspicuity. Motorcycles, which have lights of comparable power to automobiles, have long been plagued by motorists making left turns into their path. A device which modulates the headlamp beam with a low frequency to make it more noticeable has recently been found to be effective in this situation. It seems that the dual lamp system and the presence of an unlighted but visible body provide important spatial recognition factors for the automobile and hence spatial factors must also be generated for bicycles if they are to have adequate conspicuity.
Flashing lights have been used on bicycles to increase their conspicuity while minimizing power consumption. However there have been problems in the prior art in that the cyclist naturally seeks to minimize his burden and has operated such devices in lieu of a red rear tail lamp. This has led to criticisms that the cyclist may be mistakenly identified, at least at first sighting, as a construction barricade and that the cyclist's position is difficult to keep track of during the interval between flashes. The flash rate is typically in the range of once a second and they utilize either an incandescent lamp or a gas filled flash tube.
When an incandescent lamp is used, it has a relatively higher power rating since it is operating with a low duty cycle. Additionally an inrush of current is necessary in order to heat the filament to incandescence. Thus it is usually necessary to power such a flasher from batteries, either dry or rechargeable, to provide the high peak power called for.
When a gas filled flashtube is used, the energy for the subsequent flash is first stored in a high voltage capacitor. Thus it is possible for this type of device to be powered from a generator where the peak power is limited. This approach is more complex however because it requires a voltage converter to transform the low input voltage by a factor of a 100 or more times to the potential needed by the flash tube. The least expensive and most common type of voltage converter uses a transformer with a high turns ratio. A pair of transistors in a self-driven arrangement connect the DC input voltage to the primary first with one winding polarity and then with the opposite winding polarity, while the alternating voltage on the secondary is rectified to charge the storage capacitor. Since the current is limited only by the resistances in the circuit this type of converter is not very efficient. And the current draw from the source is quite heavy for the time immediately following a flash when the voltage potential of the storage capacitor is lowest. When this circuit is used in battery powered strobes, the flash rate becomes much slower as the battery is progressively consumed since the voltage conversion ratio is fixed by the transformer turns ratio.
Although the flashtube may be designed to flash when the voltage impressed upon it reached a critical value, better efficiency and longer life result from the customary design of the flashtube which requires a separate trigger circuit to initiate the flash. Energy is first stored in a smaller trigger capacitor by way of a high resistance connected to the main storage capacitor. A trigger switch element then initiates the flash by discharging the trigger capacitor into the primary of a trigger coil, the secondary of which is connected appropriately to the flash tube. The trigger switch element may be a small gas filled discharge tube, however such tubes though small and easy to wire in are somewhat expensive and have a relatively high tolerance on their breakover voltage both initially and with consideration of wearout.
An inexpensive SCR (Silicon Controlled Rectifier) may be used as the trigger switch element however it requires additional circuitry to sense the high potential on the storage capacitor and provide current into its gate terminal. Because the flash tube sometimes doesn't fire when the trigger circuit is first activated, it is necessary to have the triggering repeat until the flash does occur. This is most easily accomplished by having the trigger circuit sense the voltage on the trigger capacitor rather than that on the larger storage capacitor from which it derives it's potential. This presents no problem with the previously considered gas filled trigger tube but adds complexity in the case of the SCR because of its anode leakage currents which act to set up an unwanted feedback loop through the voltage sensing circuitry that connects the SCR anode (the trigger capacitor potential) with the SCR gate. Another complication is that the breakover devices typically used in the voltage sensing circuitry require enough current from the high voltage supply as to create a significant drain of power.
Consider a comparison of two similarly priced battery powered flashers. A flashtube type of strobe unit marketed by Bike Nashbar which comes with a strap for arm mounting and the "Belt Beacon" an incandescent unit which is detailed in U.S. Pat. Nos. 4,047,150 and 4,323,879 by Kelley. The "Belt Beacon" uses a 9 volt transistor battery which is necessary in order to make use of a bulb with a low current rating which has less mass and will heat up quickly, while the strobe uses an C-cell flashlight battery which costs less and contains more energy. The housing of the "Belt Beacon" is sealed against dust and the printed circuit board has a wax dip to protect it from moisture. In the strobe, all of the electronics including the flashtube are cast in a hemisphere of clear resin to seal out moisture and make a rugged mechanical structure. Since the cast plastic hemisphere is no larger that the C-cell, the circuit used must be quite simple and compact. When the batteries are fresh the flash rate of the strobe is about once a second, this increases to seven second intervals when the batteries become exhausted.
While in the prior art it might have been regarded as a minimal burden by non-cycling persons, the need to provide for separate mounting and replacement batteries has been as significant as their price in detering their use as a standard conspicuity measure amoung the casual bicycling public.
The flyback mode of converter circuit which is theoretically efficient has been used in DC to DC conversion for products demanding higher quality. On a repetitive basis, energy from the source is first stored in an inductor and then relased at a higher potential to the storage capacitor. The self-oscillating type which is simplest, has been detailed in U.S. Pat. No. 4,388,559 by LeFavour for use on bicycles. The flyback converter does have a variable ratio step-up; however, the self-oscillating type draws increased current from the supply if its input voltage is increased and in the time immediately following a flash it will draw a decreased amount of current owing to a lengthening of the oscillation period. Driven types of flyback converters which could eliminate these drawbacks, have in the prior art been too expensive for a bicycle application suitable for a large number of the population.
Externally powered flashers have been offered as options in the deluxe systems intended for the commuting cyclist. However, flashers meant to operate on an arbitrary source potential of the customers choice have not been available. For reasons stated previously, the flasher operating characteristics are usually dependent on the powering source voltage and impedance which are in turn dependent on the particular battery type and/or generator employed. Additionally it is customary for these systems to employ polarized connectors in the interconnections to prevent the application of reverse potentials which could damage the electronic portion of either type of flasher. Since there is no standardization of connectors or electrical power sources, this limits the use of such devices in other systems, at least for the non-technically minded casual cyclist.
It has been reported that the Swedish company, Wilhelmina Plast, is making a bicycle mostly from plastic materials and is utilizing LEDs (Light Emitting semiconductor Diodes) for the tail light, powered by batteries located in the frame. LEDs bright enough for this purpose represent an advance in semiconductor technology and have been commercially available for a considerable number of years. Such devices have the necessary beam focusing inherent in their package design and emit monochromatic light, thus not needing filters which reduce efficiency, They are available in deep red which is advantageous since it is more recognizable to motorists than the filtered incondescent, which will necessarily appear more orange-ish. When operated within their ratings, the LEDs are very long lived and are not subject to breakage from shock as is the filament of low current bulbs.
However, there are no present commercial applications of such LED devices to bicycle tail lamps in the United States. This is because the only significant advantages of the LED lies in it's inherent deep-red color output and its longevity. These are not very significant compared to a cost of 5-10 times that of an incandescent and the mood of the bicycling community today which desires improved conspicuity for such a sizeable increase in cost.
The electrical design problems inherent in the utilization of LEDs are also numerous. A single large device is with present technology impractical and thus several smaller devices must be grouped together for high outputs. When current is applied each diode produces a nearly constant voltage drop depending mostly on the particular device construction and ranges from 1.7 to 2.5 volts. This necessitates the series connection of two or three devices to avoid wasting the power available from the source. Furthermore, if only a resistor is used to limit the current, then slight voltage changes due to battery use or fluctuations in the generator speed will cause large variations in current, which is highly undesireable. It also must be considered that the LEDs operate with current of one direction only, and this creates further problems if they are to be powered from the wheel driven generator which produces alternating current.
Even if these various known known lighting methods could provide adequate conspicuity, individuals who have attempted to simultaneously use the various known visual warning devices in order to overcome the inadequacies inherent in the use of any one alone, have been derisively called "Christmas tree advocates." However, Helmut Zwahlen has performed an experiment which shows that two reflectors spaced at a distance from each other are more conspicous than a single reflector of the combined area. In the case of the pedal reflectors which are currently part of the CPSC mandated system, there is little inconvenience involved. But in general, multiple deployment has been regarded as too much trouble by the casual and serious cyclist alike. While this opinion may not be well founded, it points to the failure of the prior art to provide a practical and convenient system that is effective in solving a complex conspicuity problem but involves only a few simple to use pieces suitable also for installation and maintenance by casual cyclists and juveniles.
Minimizing the number and mounting complexity of the required pieces of the system is important both to the serious cyclist, who is likely to completely remove the system during periods when it is not needed in an effort to reduce the weight of the bicycle and improve its appearance, and to the casual cyclist who needs to have reliability with as little amount of maintenance as possible. Plastic parts, particularly the headlight lens setup, deteriorate significantly with prolonged exposure to direct sunlight and the other elements. This dictates that some removal of components pieces should be anticipated even for the casual cyclist and is currently one of the limitations of the well known generator system in which the headlamp must be a securely grounded part of the system and is thus permanently fixed.
The minimum system presently kown to be necessary includes a head lamp for illuminating the roadway, a rear warning lamp, connecting wires and the red rear facing reflector which is required by the CPSC. It is desireable to include the option of a generator in this concept of a minimum system to provide for extended periods of operation and for partial operation when the batteries are absent or discharged. Although significant improvements in batteries may be on the horizon, the most likely result of such improvements would be to reduce the monetary cost or size of a system or to provide higher power lamps rather than providing for extended periods of operation to ensure reliability under all schedules of service.
Many otherwise suitable visual warning devices have not been given serious consideration due to their size and mounting. To the uninitiated the bicycle with its exposed tubular frame seems to offer a wealth of space and attachment points. However, only the space above the rear wheel and beneath the seat is of much practical use for rear facing devices. The sweep of the rider's legs and feet eliminate the use of the chain stays except near the rear axle; attachments to the rear axle make wheel changing difficult and many bicycles are fitted with quick release rear axle assemblies which are less adaptable than the threaded type; it is difficult to get a tight grip on the small and somewhat tapered tubes that form the rear wheel support triangle; and if the attachment slips it may interfere with the rotation of the wheel as well as scratch the paint on the frame. It must also be considered that bicycles are sometimes put on the ground on their sides which tends to damage any side attachments as well as to force them inward. If a bicycle to be used for touring is fitted with panniers and a sleeping bag on top of the rack, then even the underseat position is blocked, and only the rear of the rack remains as suitable. This leads to the observation that the CPSC mandated rear reflector is currently being placed at the only effective but out of the way position that is available, not necessarily the position which would make it most effective since car headlights are necessarily aimed downwards, and research has confirmed that this would favor a lower mounting position.
Operation of a rechargeable battery together with a wheel driven generator is offered in a system made by Velo-Lux. This is accomplished by rectifying the alternating output of the generator with bridge connected diodes which charge the battery, while the lights are being powered directly from the battery. The headlight, the batteries and the rectifiers are packaged together in a unit which can be removed from the bicycle and utilized separately as a portable hand held lamp. Since the headlamp unit has most of the bulk, most of the weight, and most of the monetary value of the system, it can be expected that it will probably not be carried on the bicycle itself except when in use. Considering that the cyclist is not always able to anticipate his night time riding situations correctly, there will be times when the cyclist would like to be able to use the generator which is permanently mounted to power the rear lamp which is also permanently mounted in order to be afforded some degree of protection. However, this is not possible because the connections between the tail lamp and the generator are made within the head lamp unit and because the batteries are necessary in maintaining the proper voltage for the operation of the lamps.
The popular bicycle generator consists of a permanent magnet revolving from a drive roller in contact with the tread area of a tire and operating in conjunction with a soft iron magnetic assembly to produce an alternating magnetic flux linked to a coil of wire. The flux induces an alternating voltage in the coil whose magnitude and frequency are proportional to bicycle speed. Because the coil has inductance and, the impedance of this inductance increases with frequency which is in turn related to bicycle speed, it is possible for the alternating current, which flows through both the inductive impedance and the resistive load of the lamp bulbs, to be relatively independent of bicycle speed within the range of normal operation of the bicycle.
The unloaded voltage produced by the generator, however, is typically much higher than the normal operating voltage so that if the head lamp should burn out or become disconnected, the voltage impressed on the tail lamp increases markedly and will usually cause the burnout of the tail lamp in a short time. Some newer generator systems which make use of halogen bulbs have a voltage limiting zener device to limit the maximum voltage to the lamp and improve on the constant voltage characteristics of the generator within the normal range of bicycle with and hence this voltage limiting will become functional on the peaks of the sinusoid. Because the waveform changes with increased limiting, the burnout or disconnection of the headlamp will still allow a much increased effective or rms voltage to be impressed on the tail lamp.
In the generator system the current is limited by the inductance of the generator winding and no lasting harm will be done if the wire connecting the lamps should short out to the bicycle frame. With battery power, however, there is a possibility of a large flow of current which could cause permanent damage probably in the nature of burning the insulation off of the connecting wires.
In considering the design of generator-battery system such as the Velo-Lux it is seen that if the batteries are used as a reservoir as it were to regulate the voltage to the lamps, then it is desirable to have a battery with a large electrical capacity. However for the casual cyclist size, weight and cost are important requirements and these are best met with a lower electrical capacity battery. Increasing the size basically helps in maintaining the lamp voltage within 4 percent of nominal over most of the discharge curve. But it doesn't help in controlling the extremes of the the voltage which are determined by the chemistry involved in the battery. Considering a nickel-cadmium unit, the voltage at end of discharge may be 20 percent less than nominal and under charging conditions it will rise about 10 percent.
One of the consumer's main objections to rechargeable battery systems is the high initial cost coupled with the uncertainty of the lifetime of the battery pack under practical conditions. Of particular concern is the need to avoid completely discharging the battery which will cause the nickel-cadmium battery pack to lose capacity and even more rapid loss of useful life in the case of the sealed lead acid gelled cell. These cells, particularly the nickel-cadmium can be protected by removing the load when the potential of the battery pack falls below an amount dependent upon the number of the cells. Although the headlight is dimmer when the battery pack is exhausted to this potential there is still a very much usable amount of light being produced and it is not usually possible for the bicyclist to judge this condition properly by himself and to shut off the lamp. A complicating factor is that the nickel-cadium battery, does have a need to be occasionally excercised to this complete withdrawal of charge condition and regimens which continually make use of only a portion of the battery capacity as is commonly done with the lead acid cell will not give good results.
The Velo-Lux unit uses a halogen bulb and has improved brightness and efficiency when compared to prior art headlamps. Incandescent bulbs of which the halogen is the best example operate most effectively with a closely controlled voltage which is as large as can be tolerated without incurring unreasonably short life. Regulator circuits clearly are needed here but have not been provided in the prior art owing to complexity and expense. The low cost integrated circuit regulator which is used extensively in industry has a minimum voltage drop which greatly exceeds the 0.15 volts drop that can be achieved from a circuit employing discrete parts. On the other hand the discrete circuit has required calibration and has needed many parts to enable it to work effectively under two differing design conditions, namely as a voltage limiter when the input exceeds the lamp requirements and as a minimum voltage loss straight through element when the input voltage equals or drops below the desired lamp voltage.
The wiring for the Velo-Lux as representative of the art, is simple and straight-forward but not very convenient for the bicyclist. Two cables each containing two conductors are used to connect the tail lamp and the generator to the headlamp unit. As well as the previous problem of no direct generator operation of the tail lamp there are the additional problems of some confusion in having to connect two similarly shaped connectors to the head lamp unit and the fact that the two cables which must be routed along the tubing are not easily removeable even though the head lamp unit is itself easily removeable. Such permanent wiring is usually objectionable to the casual as well as the serious cyclist because it is obtrusive, unsightly, difficult to install and easily damaged.
On the other hand, the wiring for the well known generator system can be accomplished rather neatly since only a single small diameter wire is used in addition to the metal bicycle frame. This allows access to the interior of the frame tubing by way of drilling of holes of sufficiently small diameter so as to not affect frame strength and is available as a standard feature on some better quality bicycles. The special connectors on the ends of the cables and the larger number of holes preclude the internal to the frame routing of the cables for the Velo-Lux or other prior art systems which require multiple cable wiring.